Due to the features of miniaturization and low power consumption, a liquid crystal display (LCD) is an ideal display device for a computer, a mobile phone, etc.
In an active matrix LCD which uses thin film transistors (TFTs) to provide voltages for pixel electrodes, TFTs are disposed between pixel electrodes and corresponding data lines. By switching TFTs via gates lines, voltages supplied through the data lines can be selectively provided to the pixel electrodes. An example is described in Japanese Laid-Open Patent Publication No. 2007-188079.
For elongating the life spin of an LCD, the voltage applied between the pixel electrodes and a common electrode should be contemplated so as to avoid the situation that liquid crystal molecules always rotate in the same direction. For example, the object can be achieved by alternately inverting the voltages supplied to the liquid crystal molecules frame by frame, and/or supplying opposite voltages to the liquid crystal molecules of adjacent lines in the same frame.
FIG. 6 illustrates a gate-line driving method according to prior art, wherein the left (A) portion shows the states of gate voltage Vg, drain voltage Vd, source voltage Vs of a TFT for controlling the voltage applied to a pixel under a first driving state; and the right (B) portion shows the states of gate voltage Vg, drain voltage Vd, source voltage Vs of the TFT for controlling the voltage applied to the pixel under a second driving state.
As shown in FIG. 6, the gate voltage Vg is constant either in the first driving state or the second driving state. Therefore, in the first driving state as shown in the (A) portion, the gate voltage Vg equals to a base voltage Vg1 when the TFT is turned off, and the difference between the base voltage Vg1 of the gate voltage Vg and the drain voltage Vd is 2.3V; while in the second driving state as shown in the (B) portion, the gate voltage Vg equals to a base voltage Vg1 when the TFT is turned off, and the difference between the base voltage Vg1 of the gate voltage Vg and the source voltage Vs is enlarged to 7.5V. Accordingly, the TFT has different turn-off currents Ioff in the first driving state and the second driving state. The difference in turn-off currents Ioff would result in deteriorated image quality, e.g. flickering frames.